280 
GEOLOGY OF THE SECOND DISTRICT. 
tain, the rock is the same as upon the shore. The mountain, however, which is probably 
eight hundred feet high, is composed of the members of the Champlain group, with the ex¬ 
ception of the potsdam sandstone. It appears to have been raised directly up, and is very 
steep upon the west side, and upon which the following rocks are exposed, beginning with the 
lowest, namely, Calciferous sandrock, Chazy and Trenton limestones, Utica slate, shales of 
the Hudson river, thick-bedded grey and reddish sandstone, terminating in a grey limestone. 
The last named rocks form a perpendicular mass from eighty to one hundred feet, almost in¬ 
accessible on the west side. 
It is unnecessary to describe in detail the rocks of this group again : it will be sufficient to 
remark that they present much the same characters as at the localities already noticed; but 
being compressed into a small space, we have a better chance to inspect the whole group, 
and hence an opportunity is given for adding a few facts to those already known. 
Of the rocks which compose the great part of Snake mountain, the upper ones present some 
characters which are unknown in Essex; and, in fact, two of the members do not appear 
upon the west side of the lake, or in this county. The middle part of this mountain is occu¬ 
pied by the shales and slates of the Hudson river series, and they probably will be found four 
hundred feet thick. The upper part, or that which is exposed under these high perpendicular 
cliffs, is a mass of shining argillite, with some siliceous matter, traversed by irregular seams 
of calcareous spar, the laminae of which are quite contorted and irregularly bedded. Some of 
the layers near the junction of the grey sandstone, or grit-rock, are composed of a soft green 
slaty matter. The whole of the slaty mass exposed along the base of the cliff, is without 
fossils. We find much the same appearance at the junction here, as at other places: an 
alternation for a few feet of the two rocks, as the commencement of the one which is to suc¬ 
ceed, and then the reappearance of the mass beneath; and frequently large irregular beds, or 
portions of strata may be observed, as in the following cut (fig. 75), where a, a, are masses 
75 . 
of grit lying in the midst of the slate, insulated apparently from the mass above; and thus 
we find, for miles, the same general phenomena. The irregular alternations continue for ten 
or fifteen feet, when the thick-bedded sandstone or grit appears without interruptions of this 
kind. This mass of grit is the greywacke of authors. Some portions are brecciated, or 
belong to that variety denominated rubble, by the late Prof. Eaton. The predominant color 
of the grit is grey, but it is sometimes reddish brown. 
